While mosquitos are seen as an annoyance, from their buzzing to their itch-inducing bites, their ability to carry devastating diseases like Zika or West Nile viruses also makes them dangerous. Historically, organizations have tried to control mosquito populations by removing larvae from bodies of water where the mosquitos breed or using pesticides. Although little pesticide is needed to control these insects, its use often creates unwanted downstream effects, such as water contamination.
To to help resolve this issue, many researchers are turning to genetics to try to control mosquito populations. In new research, a team at Virginia Tech has found specific genetic targets that make some mosquito offspring inviable. Their research, published in Communications Biology, shows promise for a safer way to control and reduce mosquito populations.
A Tale of Two Species
To identify these genetic markers, the researchers bred two different species of mosquito, Ae. Aegypti, a common disease-carrying mosquito, and Ae. Mascarensis, a species based around the Indian Ocean and a cousin to Ae. Aegypti.
After creating the subsequent line offspring, the researchers bred this cross-species hybrid with one of the parent lines. They found that around 10% of this batch of offspring were completely inviable due to them being intersexed and unable to reproduce.
From this result, the researchers did several genetic analyses and found abnormalities within the cellular pathways that determine a mosquito’s sex. For this intersex offspring, the researchers found that their genetics determined them to be male, but the abnormalities in the pathway caused both male and female genes to be expressed, making them have a mix of physical traits.
According to Igor Sharakhov, a researcher on the project and professor of entomology and an affiliated faculty with the Fralin Life Sciences Institute in a recent press release: “What we found is that the morphological abnormalities start in the pupal stage during development, and in adults, the most severe cases have both testes and ovaries in one individual, which is very unusual for these species,” Sharakhov said. “Now we want to understand what causes these abnormalities.”
All Male Mosquitos to the Rescue
Based on their new findings, the researchers hope to create populations of intersex all-male mosquitos to control and reduce populations, especially in areas where these insects pass on diseases like Zika virus or dengue. These viruses are transmitted when a mosquito bites and then sucks the blood out of its prey.
Zika virus was first identified 1947 in a Rhesus macaque monkey in Uganda. After this, observations of human infection throughout Africa quickly rose. Between 1960 and 1980, Zika virus infections within Africa and Asia appeared sporadic. Then, in 2007, infections were also seen in the Americas and the South Pacific.
Thankfully, since 2017, the Zika virus has seen an overall global decline. However, its presence can lead to other, more severe health problems like Guillain-Barré syndrome, where the body’s immune system attacks the nervous system.
Unlike the Zika virus, dengue or dengue virus has been on the rise, at least in the U.S., according to the Centers for Disease Control (CDC). In 2024, global incidents of dengue have been higher than ever, as many countries worldwide are reporting higher-than-average case numbers. According to the CDC, “From January 1 – June 24, 2024, countries in the Americas reported more than 9.7 million dengue cases, twice as many as in all of 2023 (4.6 million cases).”
Because of these growing cases, scientists are working overtime to find innovative solutions to control and reduce disease-carrying mosquito populations.
For the Virginia Tech researchers, seeing the abnormalities in their male mosquitos could be the exact solution.
“What we found is that the morphological abnormalities start in the pupal stage during development, and in adults, the most severe cases have both testes and ovaries in one individual, which is very unusual for these species,” Sharakhov said in the press release. “Now we want to understand what causes these abnormalities.”
By studying the sex-determining pathways within the mosquitos, the researchers can work to try to create their all-male mosquito population. This population could even breed with wild populations, passing on the genetic traits to their offspring.
“Since the intersex is genetically male but expresses female transcripts, it provides a system to identify genes affecting female behavior, which can be useful for future vector control strategies,” Jiangtao Liang, a postdoctoral associate in entomology explained in the press release. “Intersexes can serve as a valuable model for the discovery of genetic factors involved in sex determination, sexual differentiation, mating, host-seeking, and blood-biting behaviors in mosquitoes.
Finding new sex determination pathway genes and their disruptions in mosquitoes will contribute to the effective control of disease vectors through genetic manipulations based on sex separation.”
Kenna Hughes-Castleberry is the Science Communicator at JILA (a world-leading physics research institute) and a science writer at The Debrief. Follow and connect with her on X or contact her via email at kenna@thedebrief.org